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Several Patterns (several + pattern)
Selected AbstractsPollen,plant,climate relationships in sub-Saharan AfricaJOURNAL OF BIOGEOGRAPHY, Issue 3 2007Julie Watrin Abstract Aim, To demonstrate that incorporating the bioclimatic range of possible contributor plants leads to improved accuracy in interpreting the palaeoclimatic record of taxonomically complex pollen types. Location, North Tropical Africa. Methods, The geographical ranges of selected African plants were extracted from the literature and geo-referenced. These plant ranges were compared with the pollen percentages obtained from a network of surface sediments. Climate-response surfaces were graphed for each pollen taxon and each corresponding plant species. Results, Several patterns can be identified, including taxa for which the pollen and plant distributions coincide, and others where the range limits diverge. Some pollen types display a reduced climate range compared with that of the corresponding plant species, due to low pollen production and/or dispersal. For other taxa, corresponding to high pollen producers such as pioneer taxa, pollen types display a larger climatic envelope than that of the corresponding plants. The number of species contained in a pollen taxon is an important factor, as the botanical species included in a taxon may have different geographical and climate distributions. Main conclusions, The comparison between pollen and plant distributions is an essential step towards more precise vegetation and climate reconstructions in Africa, as it identifies taxa that have a high correspondence between pollen and plant distribution patterns. Our method is a useful tool to reassess biome reconstructions in Africa and to characterize accurately the vegetation and climate conditions at a regional scale, from pollen data. [source] Early NMDA receptor-driven waves of activity in the developing neocortex: physiological or pathological network oscillations?THE JOURNAL OF PHYSIOLOGY, Issue 1 2010Camille Allene Several patterns of coherent activity have been described in developing cortical structures, thus providing a general framework for network maturation. A detailed timely description of network patterns at circuit and cell levels is essential for the understanding of pathogenic processes occurring during brain development. Disturbances in the expression timetable of this pattern sequence are very likely to affect network maturation. This review focuses on the maturation of coherent activity patterns in developing neocortical structures. It emphasizes the intrinsic and synaptic cellular properties that are unique to the immature neocortex and, in particular, the critical role played by extracellular glutamate in controlling network excitability and triggering synchronous network waves of activity. [source] THE POPULATION GENETICS OF ADAPTATION: THE ADAPTATION OF DNA SEQUENCESEVOLUTION, Issue 7 2002H. Allen Orr Abstract I describe several patterns characterizing the genetics of adaptation at the DNA level. Following Gillespie (1983, 1984, 1991), I consider a population presently fixed for the ith best allele at a locus and study the sequential substitution of favorable mutations that results in fixation of the fittest DNA sequence locally available. Given a wild type sequence that is less than optimal, I derive the fitness rank of the next allele typically fixed by natural selection as well as the mean and variance of the jump in fitness that results when natural selection drives a substitution. Looking over the whole series of substitutions required to reach the best allele, I show that the mean fitness jumps occurring throughout an adaptive walk are constrained to a twofold window of values, assuming only that adaptation begins from a reasonably fit allele. I also show that the first substitution and the substitution of largest effect account for a large share of the total fitness increase during adaptation. I further show that the distribution of selection coefficients fixed throughout such an adaptive walk is exponential (ignoring mutations of small effect), a finding reminiscent of that seen in Fisher's geometric model of adaptation. Last, I show that adaptation by natural selection behaves in several respects as the average of two idealized forms of adaptation, perfect and random. [source] Toward a reduction of the bimolecular reaction model for titan's ionosphereINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2008Nathalie Carrasco The aim of this paper is to highlight the skeletal chemistry responsible for the rich ionospheric chemistry observed in Titan's atmosphere. The present database is represented by about 700 ion,molecule reactions, which are not all important to describe the system. Our criterion to reduce the list of reactions is to reproduce a reference mass spectrum within its uncertainties. This reference mass spectrum is obtained with the complete reaction database and with neutral densities optimized for the INMS mass spectrum measured at 1200 km during the T5 flyby. We compared two mechanism reduction methods, brute force screening and global sensitivity analysis. The analysis of the residual scheme with only 35 bimolecular reactions highlights several patterns, concerning in particular ionic growth processes and introduction of nitrogen to the ionic species. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 699,709, 2008 [source] Review of plant biogeographic studies in BrazilJOURNAL OF SYSTEMATICS EVOLUTION, Issue 5 2009Pedro FIASCHI Abstract, Molecular phylogenetic studies have become a major area of interest in plant systematics, and their impacts on historical biogeographic hypotheses are not to be disregarded. In Brazil, most historical biogeographic studies have relied on animal phylogenies, whereas plant biogeographic studies have largely lacked a phylogenetic component, having a limited utility for historical biogeography. That country, however, is of great importance for most biogeographic studies of lowland tropical South America, and it includes areas from a number of biogeographic regions of the continent. Important biogeographic reports have been published as part of phylogenetic studies, taxonomic monographs, and regional accounts for small areas or phytogeographic domains, but the available information is subsequently scattered and sometimes hard to find. In this paper we review some relevant angiosperm biogeographic studies in Brazil. Initially we briefly discuss the importance of other continents as source areas for the South American flora. Then we present a subdivision of Brazil into phytogeographic domains, and we cite studies that have explored the detection of biogeographic units (areas of endemism) and how they are historically related among those domains. Examples of plant taxa that could be used to test some biogeographic hypotheses are provided throughout, as well as taxa that exemplify several patterns of endemism and disjunction in the Brazilian angiosperm flora. [source] Co-evolution of invention activities among cities in New England,PAPERS IN REGIONAL SCIENCE, Issue 1 2006Catherine Y. Co Patent; invention; city; New England Abstract., This article examines how patent activities in metropolitan areas change using New England as a backdrop. Using U.S. patent data from 1975 to 1999, this article uncovers several patterns. First, some patent-lagging cities catch up with patent-leading cities. Second, one contributory factor for catch up is knowledge diffusion. Third, shakeouts in patent specialisations in leading cities are less dramatic compared to those in lagging cities. Fourth, invention activities among cities co-evolve. The co-evolution of invention activities among cities provides an incentive for city and/or state governments to coordinate policies that may affect knowledge creation in their jurisdictions. [source] | |||||||||||||